Self expanding vascular endoprosthesis for aneurysms

ABSTRACT

A self expanding vascular endoprosthesis for aneurysms comprising a sheet of a resiliently flexible biocompatible material, such as polypropylene which sheet has been rolled upon itself about one of its longitudinal edges. The tightly rolled endoprosthesis is introduced in the end of the catheter through a contiguous artery into the artery having the aneurysm. After ejection from the catheter at a suitable point in the artery the endoprosthesis expands to form a bridge isolating the aneurysm from the arterial blood flow. The endoprosthesis stimulates cellular proliferation in the adjacent vascular tissue which assists in forming a seal between the endoprosthesis and the vascular tissue. The resultant endothelial growth also assists in maintaining the endoprosthesis in position in the artery.

FIELD OF THE INVENTION

The present invention relates to a self expanding vascularendoprosthesis for aneurysms and to apparatus and a method forintroducing such an endoprosthesis into an artery.

BACKGROUND ART

An Aneurysm is the focal abnormal dilation of an artery. Thecomplications which arise from aneurysms are specifically rupture,embolisation, fistularisation and symptoms related to pressure onsurrounding structures. Aneurysms are commonly found in the abdominalaorta, being that part of the aorta which extends from the diaphragm tothe point at which the aorta bifurcates into the common iliac arteries.These abdominal aortic aneurysms typically occur between the point atwhich the renal arteries branch from the aorta and the bifurcation ofthe aorta.

The standard treatment for aneurysms is to resect them by opening theaneurysm directly and inserting an inlaid graft made of a biocompatiblematerial such as Dacron. The operation in most cases is large entailingconsiderable blood loss, at least 10 days in hospital and a mortalityrate of about 5% in elective cases. This mortality rate is normallyrelated to associated vascular problems such as myocardial infarction.Many patients cannot be subjected to such a large procedure because ofintercurrent disease and therefore die of the aneurysm or thecomplications thereof.

It has been proposed by Balka etal. (Journal of Surgical Research 40305-309 (1986)) to treat abdominal aortic aneurysms by the insertion ofan intraluminal prosthesis, which approximates the diameter of the aortaabove and below the aneurysm, into the aorta through the common femoralartery. In this case the prosthesis comprised a polyurethane tube with anitinol and/or stainless steel frame which was designed in such aconfiguration that it can be compressed inside a catheter and thenregain its original shape after being discharged into the aorta. Thisproposal does not appear to have been adopted for the treatment ofhumans due to difficulty in ensuring that the prosthesis will expandsufficiently to form a seal with the aorta above and below the aneurysm.The present inventor has developed a prosthesis which provides analternative to that proposed by Balka et al.

In a first aspect the present invention consists in a self expandingvascular endoprosthesis adapted to bridge across an aneurysm in anartery, the endoprosthesis comprising a substantially imperforate sheetof a resiliently flexible biocompatible material, the sheet being rolledupon itself about one of its longitudinal edges, the material from whichthe sheet is formed being such that

(a) upon being introduced into an artery the endoprosthesis willresiliently expand of its own volition to press firmly against theinternal wall of the artery to bridge across the aneurysm and to fluidisolate it from blood flowing in the artery, and

(b) the endoprosthesis has sufficient longitudinal stiffness that therewill be a compliance mismatch between the endoprosthesis and the wall ofthe artery to induce sufficient cellular proliferation in that walladjacent the ends of an implanted endoprosthesis to cause theendoprosthesis to be adhered to the arterial wall.

In a second aspect the present invention consists in apparatus forintroducing a self expanding vascular endoprosthesis for aneurysms intoan artery, comprising an elongate tubular catheter, a self expandingvascular prosthesis for aneurysms according to the present inventiondisposed within the catheter and means for ejecting the endoprosthesisfrom the catheter.

In a third aspect the present invention consists in a method fortreating an aneurysm in an artery by introducing a self expandingendoprosthesis into the artery, the method comprising the steps of:

inserting one end of a catheter containing a self expanding vascularendoprosthesis according to any one of claims 1 to 5 into an arterycommunicating with the artery having the aneurysm,

moving the catheter along the patient's vascular system until the end ofthe catheter is adjacent the aneurysm,

ejecting the endoprosthesis from one end of the catheter such that itbridges across the aneurysm and expands firmly into contact with thewall of the artery so that the aneurysm is fluid isolated from bloodflowing in the artery, and

causing the endoprosthesis to be held in position bridging across theaneurysm by cellular proliferation of the wall of the artery caused bythe compliance mismatch between the endoprosthesis and the wall of theartery.

The endoprosthesis is preferably formed from a substantially rectangularsheet of a suitable grade of polypropylene or another similar syntheticplastics material. The sheet preferably has a thickness of from 0.01 mmto 0.8 mm, more preferably 0.3 mm to 0.5 mm. The corners of the sheetwhich are on the outside of the prosthesis are preferably rounded toavoid ulceration of the arterial wall. The length of the sheet must besufficient to bridge the aneurysm but is preferably sufficient that oneend rests against a bifurcation of the artery in which the aneurysmoccur. This latter preferment assists in retention of the endoprosthesisin a position in which it bridges over the aneurysm. still allowingblood supply to the diverging vessels.

In another embodiment of the invention the endoprosthesis is such thatupon release from the end of the catheter it is capable of increasing inlength as well as expanding radially outwardly. The sheet forming theendoprosthesis might have a "memory" causing it to want to expand fromits rolled up cylindrical form into a helical form of greater diameterthan the initial cylinder and of greater length. The overlapping turnsof the expanded helical coil serving to prevent fluid communicationbetween the interior of the endoprosthesis and the aneurismal sac. Inanother form of the invention the sheet forming endoprosthesis may be ofa very thin film having ribs which assume a helical form when releasedfrom the endoprosthesis. The advantage of an endoprosthesis which canincrease in length after release from the catheter is that it is easierto thread a catheter containing such a shortened endoprosthesis throughthe patient's vascular system to the point of the aneurysm.

The sheet of material from which the endoprosthesis is rolled uppreferably has a compliance mismatch with the vascular tissue and ispreferably quite stiff in a longitudinal direction. This is believed tohave the effect of stimulating a reaction in the arterial wall andthereby inducing cellular proliferation in the vascular tissuesurrounding the ends of the endoprosthesis. This causes a proliferationof endothelial cells which has the effect of adhering the endoprosthesisto the arterial wall. The endoprosthesis thus has a self suturing effectwhich retains it against movement along the artery.

The material from which the endoprosthesis is formed should beresiliently flexible so that upon being released from the constraint ofthe catheter the prosthesis will expand to bear against the arterialwall above and below the aneurysm. The use of the sheet of materialrolled up along one of its side edges to form a scroll has been found toallow the prosthesis to expand very considerably if need be. Thisfeature is important because the neck of the aneurysms tend to varygreatly between patients. Also depending upon where the ends of theendoprosthesis extend to the size of the native artery may be quitesmall or quite large. It is important that the endoprosthesis does notocclude vessels extending laterally from the artery and thus it may benecessary to terminate the endoprosthesis in a mildly distended part ofthe aneurysm. For this reason it may be necessary for the endoprosthesisto expand not merely to the normal diameter of the artery but towhatever extent is necessary to form a seal with the artery at eitherend of the aneurysm so that systalic blood pressure is not transmittedto the aneurysmal sac formed between the endoprosthesis and thedistended arterial wall.

In the case of the abdominal aorta the normal internal diameter of theaorta is about 18 mm. Abdominal aortic aneurysms will typically have adiameter of from 40 to 70 mm. The abdominal aorta between the renalarteries and the iliac arterial bifurcation is typically about 110 mm.The aneurysm normally extends along a substantial portion of theabdominal aorta and is bounded at either end by a neck of undistendedarterial wall adjacent the renal arteries and adjacent the iliacarterial bifurcation. In this case then the prosthesis is preferablyrolled up from a sheet of polypropylene having a thickness of 0.4 mm, alength of 110 mm and a width of from 98 mm to 142 mm. It should berecognized however that the neck of the aneurysms tend to be veryvariable and it may be necessary to use a sheet wider than thatindicated to form the endoprosthesis.

The present inventor has found that the endoprosthesis according to thepresent invention may be rolled up to a very small diameter allowing itsintroduction into a deep artery, such as the abdominal aorta, from amore superficial but much smaller artery, such as the common femoralartery.

The apparatus according to the present invention comprises aconventional catheter into which the endoprosthesis has been inserted ina rolled up condition and means to eject the endoprosthesis from an endof the catheter. The apparatus may also include a guide wire and/orsensing means to assist in the determination of the correct position atwhich the endoprosthesis should be ejected from the catheter. Theejection of the endoprosthesis from the catheter may be achieved byholding the catheter stationary and pushing the endoprosthesis from itusing a plunger extending down the catheter or the plunger may beabutted against the proximal end of the endoprosthesis and the catheterwithdrawn from around the endoprosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter given by way of example is a preferred embodiment of thepresent invention described with reference to the accompanying drawingsin which:

FIG. 1 is a front elevational view of a sheet of material suitable forforming into a self expanding vascular endoprosthesis according to thisinvention;

FIG. 2 is a perspective view of the sheet of FIG. 1 which has beenrolled into the form of a self expanding vascular endoprosthesisaccording to this invention on a suitable forming tool;

FIG. 3 is a longitudinal sectional view of a catheter containing a selfexpanding vascular endoprosthesis according to this invention and adevice for ejecting the prosthesis from the catheter;

FIG. 4 is a diagrammatic ventral view of a patient showing a vascularendoprosthesis according to the invention in position spanning anabdominal aortal aneurysm;

FIG. 5 is a cross-sectional view along V--V of FIG. 4;

FIG. 6 is a cross-sectional view along VI--VI of FIG. 4; and

FIG. 7 is a cross-sectional view of a self expanding vascularendoprosthesis according to the present invention in position in thethoracic aorta of a patient.

BEST METHOD

The sheet 10 of FIG. 1 is formed of surgical grade, imperforatepolypropylene having a thickness of 0.4 mm, a width of 120 mm and alength of 110 mm with rounded corners. The sheet 10 is preferably rolledup into a self expanding vascular endoprosthesis on a tool 11 having ahandle 12 and, extending axially from it, a bifurcated rod 13. A sleeve14 is slidable disposed on the rod 13. In use one side edge of the sheet10 is slid between the bifurcation of the rod 13 and the tool 12 rotatedto roll the sheet 10 about the rod 13. After being tightly rolled ontothe rod 13 the sheet 10, now formed into an endoprosthesis, is insertedinto the proximal end of a suitable catheter 15. The tool 12 can then bedisengaged from the endoprosthesis 10 by positioning the collar 14against the end of the endoprosthesis 10 and withdrawing the rod 13 fromwithin the rolled up endoprosthesis 10. The endoprosthesis 10 is nowready for insertion into a patient.

FIG. 4 shows a typical abdominal aortic aneurysm into which anendoprosthesis 10 has been inserted. The abdominal aorta 16 has becomedistended to from an aneurysm 17 between the renal arteries 18 and thepoint at which the aorta 16 bifurcates to form the left and right iliacarteries 19. The endoprosthesis 10 is introduced to bridge the aneurysm17 between a neck 21 adjacent the renal arteries 18 and a neck 22adjacent the iliac arteries 19. This introduction is achieved by givingthe patient a local anaesthetic in the region of one of the commonfemoral arteries 23 and introducing the catheter 15 through that arteryand through the contiguous iliac artery into the aorta 16. The positionof the tip of the catheter 15 relative to the renal arteries 18 needs tobe known accurately to prevent the endoprosthesis 10 being introducedinto the aorta 16 at a level where its upper end will occlude the renalarteries or where its lower end will expand in one of the iliac arteries19. This is achieved in a manner known per se by angiography or by theintroduction of an endoscope or some other form of inter-luminal ortranscutaneous imaging system (not shown) through the catheter 15.

After the tip of the catheter 15 has been correctly positioned in theaorta 16 the endoprosthesis is ejected from the catheter 15 into theaorta 16. This is preferably achieved by positioning an ejector 24 inthe catheter 15 with an end portion 25, which forms a close sliding fitwith the catheter 15, abutting against the end of the endoprosthesis 10.The catheter 15 is then carefully withdrawn. As it is ejected from thecatheter 15 the natural resilience of the endoprosthesis 10 causes it toexpand until it bears firmly against the aorta 16 at its narrowestpoints, in this case the neck 25, portions 21 and 22 (see FIG. 5). Theexpanded endoprosthesis 10 will form a tube bridging the aneurysm 17 toform an aneurysmal sac between the endoprosthesis 10 and the aorta 16 inthe region of the aneurysm 17 which is not in fluid communication withthe arterial blood flow (see FIG. 6).

It is believed that the stiffness of the synthetic plastics materialfrom which the endoprosthesis 10 is formed will induce cellularproliferation in the aortal wall adjacent the ends of the endoprosthesis10. This cellular proliferation assists in holding the endoprosthesis 10in place in the aorta 16.

As is seen in FIG. 7, if it is desired to preserve blood flow from anartery 26, such as the thoracic aorta, into a diverging blood vessel 27,such as the spinal artery, an endoprosthesis 28 may be introduced intothe artery 26 which has a width less than the circumference of theartery. In this case the isolation of the aneurysm from the arterialblood flow relies upon the endoprosthesis forming a seal with the insideof the artery 26 on either side of the diverging blood vessels 27.

It can be seen from the foregoing that the use of the endoprosthesisaccording to this invention, and the method according to this inventioncan dramatically simplify the treatment of aneurysms. It also allowstreatment of patients with concurrent disease states which would nototherwise be amendable to treatment at all.

I claim:
 1. A self expanding vascular endoprosthesis adapted to bridgeacross an aneurysm in an artery, the endoprosthesis comprising asubstantially imperforate sheet having at least one longitudinal edgeand being made of a resiliently flexible biocompatible material, thesheet being rolled upon itself about a longitudinal edge to form anendoprosthesis having two ends, one at either end of the longitudinaledge, the sheet having an inner surface and an outer surface each ofwhich is smooth and free of ribs or other projections that would impedethe resilient expansion of the endoprosthesis into contact with aninternal wall of the artery both above and below the aneurysm, thematerial from which the sheet is formed being such that(a) upon beingintroduced into an artery the endoprosthesis will resiliently expand dueto its resilient flexibility to press firmly against an internal wall ofthe artery both above and below the aneurysm to bridge across theaneurysm and to fluid isolate it from blood flowing in the artery, and(b) the endoprosthesis having sufficient longitudinal stiffness suchthat there will be a compliance mismatch between the endoprosthesis anda wall of the artery to induce sufficient cellular proliferation in thatarterial wall adjacent the ends of an implanted endoprosthesis to causethe endoprosthesis to be adhered to the arterial wall.
 2. Anendoprosthesis as claimed in claim 1, in which the endoprosthesis isformed from a sheet of a synthetic plastics material.
 3. Anendoprosthesis as claimed in claim 2, in which the endoprosthesis isformed from a sheet of polypropylene having a thickness of from 0.01 to0.8 min.
 4. An endoprosthesis as claimed in claim 3, in which theendoprosthesis is formed from a sheet of polypropylene having athickness of from 0.3 to 0.5 min.
 5. An endoprosthesis as claimed inclaim 1, in which the sheet is substantially rectangular having twosubstantially parallel longitudinal edges and has a width, as measuredbetween the longitudinal edges, of from 1.75 to 2.5 times thecircumference of the artery into which the endoprosthesis is to beintroduced, which circumference is measured above the aneurysm.
 6. Anendoprosthesis as claimed in claim 5, which the circumference ismeasured below the aneurysm.